In recent years, in order to improve an accuracy of forming a tire, a method of manufacturing the tire using a rigid inner mold (hereinafter it may be referred to as “a rigid inner mold method”) has been proposed (e.g. see Patent Documents 1 and 2). The rigid inner mold comprises an inner mold body having an outer shape suiting a shape of a tire cavity surface of a vulcanized tire. Onto the inner mold body, tire structure members are sequentially attached so as to form a green tire. The green tire with the rigid inner mold is put into a vulcanizing metallic mold, and the green tire is vulcanized and molded.
As shown in FIG. 8 (A), in the rigid inner mold method, in order to extract an inner mold body (a) from the tire after vulcanization molding, the inner mold body (a) is divided into a plurality of inner mold segments (c) in the circumferential direction.
The inner mold segments (c) comprises first inner mold segments c1 where both of circumferential end surfaces are defined as first mating surfaces sc1 each having a small width in the circumferential direction, and second inner mold segments c2 where both of end surfaces are defined as second mating surfaces sc2 each having a large width in the circumferential direction. The first mating surface sc1 and the second mating surface sc2 which lie circumferentially next to each other are butted with each other, thereby the inner mold body (a) is formed as an annular shape.
The first mating surface sc1 is formed as an outward inclination surface inclined in the direction of which circumferential width increases toward the radial by inward. The second mating surface sc2 is formed as an inward inclination surface inclined in the direction of which circumferential width decreases toward the radial by inward. Thus, the segments can be taken out one by one by moving radially inwardly commencing with the first inner mold segment c1. That is, it makes possible to disassemble and to take out the inner mold body (a) from the tire.
However, a temperature of the inner mold body (a) rises from an ordinary temperatures state at a time of the green tire formation (about from 15 to 50° C.) to a high temperature state at a time of vulcanization (not less than 100° C.). Therefore, at the time of vulcanization, thermal expansion causes a pressing force between the inner mold segments c1 and c2 which lie next to each other in the circumferential direction. At this time, as shown in FIG. 8 (B), the first inner mold segment c1 which comprises the mating surface sc1 as an outward inclination surface is pushed out radially inward. The inner mold segment c2 which has the mating surface sc2 as an inward inclination is pushed out radially outward. As a result, the radial step (d) generates between the outer peripheral surfaces of the first and second inner mold segments c1 and c2, thereby causing a problem of reducing the uniformity of the tire.
To reduce the step (d), it is proposed to increase an interspace amount between the mating surfaces sc1 and sc2 at the ordinary temperatures state so as to reduce the pressing force during the vulcanization molding. However, this case leads to a decrease in the tire quality such as the rubber stuck cased by rubber flowing into the interspace during the vulcanization.